Iron complexes which have, in the molecule thereof, a Schiff base-containing ligand structure and an iron atom have been conventionally used in industry as additives for resins, pharmaceuticals and catalysts. Some known iron complexes which have a Schiff base-containing ligand structure and an iron atom in the molecule are: iron complexes which have a Schiff base-containing ligand structure and one iron atom in the molecule (hereinafter, such complexes will be referred to as iron mononuclear complexes); and iron complexes which have, in the molecule thereof, a structure having two iron atoms bonded to each other via one oxygen atom and a ligand structure containing a Schiff base (hereinafter, such complexes will be referred to as iron dinuclear complexes). Iron dinuclear complexes outperform iron mononuclear complexes in some applications. When, for example, these iron complexes are used as additives in epoxy resin compositions, the iron dinuclear complexes allow the compositions to exhibit higher flame retardance and higher fluidity than the compositions containing the iron mononuclear complexes. Further, when the iron complexes are used as magnetic carriers for drug delivery systems such as anticancer drugs, the iron dinuclear complexes are known to have high magnetic properties and be suited as carriers compared to the iron mononuclear complexes.
Numerous methods for producing iron dinuclear complexes have been heretofore presented. For example, Patent Literature 1 describes a method for producing an iron dinuclear complex for use as a catalyst wherein salicylaldehyde, ethylenediamine and ferrous sulfate heptahydrate are dissolved into water, the solution is heated, and the resultant black brown precipitate of reaction product is recrystallized from pyridine/ethanol solvent to give [Fe(C16H14N2O2)]2O.
Patent Literature 2 describes a method for producing an iron dinuclear complex for use as an additive for enhancing the flame retardance and fluidity of epoxy resin compositions. Specifically, it is described that salicylaldehyde, ethylenediamine and iron sulfate are dissolved into pure water, and the solution is allowed to stand at 110° C. for 3 hours, cooled and filtered to give an iron dinuclear complex.
Patent Literature 3 describes a method for producing an iron dinuclear complex for use as a magnetic carrier for a drug delivery system such as anticancer drug. Specifically, it is described that a ligand synthesized from a salicylaldehyde derivative and ethylenediamine, and triethylamine are dissolved into methanol, the resultant solution is combined with a methanol solution of ferric chloride, and the resultant compound is washed and recrystallized as an iron dinuclear complex.
As known in the art, the transesterification between a carboxylate ester and an alcohol compound is conventionally performed under catalysis of an iron complex having, in its molecule, a Schiff base-containing ligand structure and an iron atom.
For example, Patent Literature 1 describes that methyl methacrylate is transesterified with an alcohol compound having a primary hydroxyl group or a secondary hydroxyl group in the presence of an iron catalyst, thereby forming the methacrylate ester compound of the alcohol compound having a primary hydroxyl group or a secondary hydroxyl group.